The present invention relates generally to dampers and more particularly to thermally operated dampers for fire and smoke air flow control systems.
Conventionally, blade type dampers are employed to control the flow of air, smoke or fire through a diffuser or duct system during fire conditions. In a typical smoke control system, the damper blades of some dampers in the system are actuated to a fully opened position during fire conditions to allow smoke to be exhausted through specific ducts. The damper blades of other fire control dampers are displaced to their fully closed position during fire conditions to prevent the passage of smoke and fire through specific ducts.
Such prior art smoke or fire dampers are typically provided with means for remote control so that they may be selectively activated such as by a fire alarm system. Such smoke or fire dampers are placed at selected positions in a duct system, often in addition to the normal environmental air flow dampers.
The remote control of such fire and smoke dampers by electrical motors oriented outside the damper is common. Such motor activated dampers are relatively expensive to purchase and install. Also, the motors and wiring for such systems are difficult and expensive to install and maintain. Such control systems must be of first rate quality in order that reliable operation, often times years after installation in a dirty environment under extremely hostile conditions, can be expected.
Conventionally, such dampers in addition to means to activate the unit in response to remote signals also include means to respond to excessive temperature increases in the vicinity of the device. It has long been known that such dampers may be spring operated using cables attached to block or bracket linkages within the damper. The cables are normally threaded through a ferule disposed in the duct wall to reach an operator motor outside of the duct in which the damper is located. Springs are used t bias the blades towards a closed position, as for example, springs extending between the damper frame and the blade provided with a fusible link. The fusible link breaks in response to excessive temperature and allows the spring to move the blade or blades to a closed position whereupon the passage of fire through the duct system will be halted. The cable and operator motor allow reopening of the duct when desired. Similar arrangements have also been used to provide dampers which move to the fully opened position in response to selected stimulus and for air dampers wherein the blades are set to normally operate at an intermediate partially opened position.
Alternatively, it is known to operate dampers through a damper operator shaft the rotation of which corresponds to the rotation of the damper blades. See, for example, the structure and various damper operators disclosed and discussed in my prior issued U.S. Pat. No. 4,113,332 entitled "Smoke, Fire and Air Control Dampers with Stamped Blades".
The use of over center knee-action locking arrangements in either cable or shaft actuated dampers is disclosed in my prior issued U.S. Pat. No. 4,338,967 entitled "Universal Link Bar Operator and Actuator for Rotating Blade Air, Smoke and Fire Dampers" and the related applications disclosed therein which are incorporated herein by references as if fully disclosed herein.
The electric or pneumatic controls conventionally employed with such dampers are expensive to install and maintain. Further, such prior devices typically were limited to low temperature use, and were slow or unable to react to fire conditions or remote signals and did not automatically reset when the fire conditions were removed.